Note: Descriptions are shown in the official language in which they were submitted.
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5MOLTEN METAL PUMP WITH VANED IMPELLER
AND FLOW DIRECTING PUMPING CHAMBER
FIELD OF THE INVENTION
This invention relates to molten metal pumps, and more
particularly, to pumps utilizing a vaned impeller.
15BACKGROUND OF THE INVENTION
In the processing of molten metals, it is often necessary to
pump molten metal from one place to another. When it is desired to remove
molten metal from a vessel, a so-called transfer pump is used. When it is
20 desired to circulate molten metal within a vessel, a so-called circulation pump
is used. When it is desired to purify molten metal disposed within a vessel, a
so-called gas injection pump is used. In each of these pumps, a rotatable
impeller is disposed within a volute case accessible to the molten metal in the
vessel. Upon rotation of the impeller within the volute, the molten metal is
25 pumped as desired in a direction permitted by the volute.
In each of the pumps referred to, the impeller is disposed within
the volute formed in a base member. Typically the volute in the base member
is suspended within the molten metal by means of posts. The impeller is
supported for rotation in the base member by means of a rotatable shaft. The
30 base member includes an outlet passage in fluid communication with the
impeller, and upon rotation of the impeller, molten metal is drawn into the
volute and the open section of the impeller, where it then is discharged under
pressure to the outlet passage.
Although pumps previously known in the art operate
35 satisfactorily to pump molten metal from one place to another, certain
problems have not been addressed.
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Particularly, these problems relate to the efficiency of the impeller, duration of
operability and consistency of performance.
U.S. Patent No. 4,940,384 shows a molten metal pump with a
cup-like impeller body having vanes and lateral openings for moving molten
metal. Although the impeller of this pump transports molten metal, it is prone
to clogging by foreign materials such as semi-solids and solids, e.g. drosses,
refractory debris, metallic inclusions, etc., (herein after referred to as
"particles") contained in the vessel and frequently drawn into the molten metal
pump. If a large particle is drawn into the pump, the impeller can be jammed
against the volute case, causing catastrophic failure of the pump. Even if
catastrophic failure does not occur, small particles eventually clog the lateralopenings and degrade the performance of the impeller by reducing the
volume of molten metal it can transfer. Accordingly, it is desirable in the art to
have an impeller which minimizes clogging, thereby maintaining high
efficiency over time and avoiding catastrophic failure.
Impeller-type equipment without lateral openings has been
utilized in molten metal stirring and/or submersion types of devices. U.S.
2 o Patent No. 4,898,367 shows a gas dispersion rectangular block without
openings. However, this stirring device does not achieve a directed, forced
fluid flow. Particularly, the impeller must be rotatable within a housing to
maximize forced flow from the impellers rotation. In addition to block type
molten metal agitation devices, vaned circular equipment has been used, see
U.S. Patent No. 3,767,382. Again, however, there is no means for achieving
forced directional molten metal flow. Such forced
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directional molten metal flow is highly necessary in the
application of pumping technology in molten metal
processing. In a circulation mode, better convectional
heat transfer occurs (greater kinetic energy imparted by
the pump), and faster melting exists as solid charge
materials such as scrap or ingot is mixed more quickly
and thoroughly into and with the liquid metal. In a
transfer mode, the liquid metal is more strongly directed
or redirected into a conveying conduit such as a riser or
pipeline for more efficient transfer at a higher rate as
a result of such improved forced directional molten metal
flow.
In summary, the molten metal treatment art
described in the above two paragraphs fails to achieve
important advantages of the current invention.
Particularly, either there is no effective prevention of
clogging and/or there is no means to achieve directional
forced molten metal flow.
The current invention achieves a number of
advantages in directional forced molten metal flow. The
impeller of the current pump is not prone to clogging of
lateral openings as in prior pump impellers. According-
ly, catastrophic failure is much less likely to occur and
the efficiency of the impellers operation does not
degrade as rapidly over time. The design also achieves
high strength by increasing the load area material
thickness.l Furthermore, the impeller design permits easy
manufacturing processes. Accordingly, it reduces the
cost of production and allows a wide selection of
impeller material, such as graphite or ceramic. Also,
the current impeller concept is adaptable to allow
optimization as required without large scale
manufacturing alteration.
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SUMMARY OF THE INVENTION
Accordingly, it is an object of an aspect of
this invention to provide a new and improved molten metal
pump.
It is an objective of this invention to provide
a new and improved impeller for use in a molten metal
pump.
To achieve the foregoing objects and in
accordance with an aspect and purpose of the invention as
embodied and broadly described herein, the molten metal
pump of this invention comprises an elongated drive shaft
having first and second ends, the first end extending out
of a molten metal bath and the second énd extending into
the molten metal bath. An impeller is attached to the
second end of the drive shaft. The impeller has a solid
circular base portion with at least one face and at least
two vanes extending substantially perpendicular from
said face. Preferably, the vanes also extend radially
from the center of the face. Solid as used herein means
a lack of openings capable of accommodating molten metal
flow. Face as used herein means a relatively flat
surface. The impeller is disposed within a volute having
an inlet into which molten metal can be drawn and an
outlet through which molten metal can be forcibly
discharged by the impeller's rotation. Volute as used
herein means a casing which facilitates the impeller's
convergence and expulsion of molten metal.
Other aspects of this invention are as follows:
A molten metal pump comprising:
(a) a shaft having first and second ends;
(b) a means for rotating said shaft in
com~llnication with said first end of said shaft;
(c) an impeller in comm~lnication with said
second end of said shaft;
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(d) a base member housing said impeller in a
pumping chamber, wherein said pumping chamber has a
first opening through which molten metal can be drawn
and a second opening through which molten metal can
be discharged; and
(e) said impeller comprising an imperforate
substantially circular base having a surface facing
toward a first end of the shaft, and at least two
imperforate vanes conn~cted to and exten~; ng
substantially perpendicular from said surface and
ext~n~;ng radially from said shaft or a hub securing
said shaft toward a peripheral portion of said basie,
said vanes being spaced circumferentially apart;
each vane defining a first edge, a second edge
and a third edge;
said first edge being disposed on said base;
said second edge defining an inlet end;
said third edge being a radially outer edge;
said second edge of adjacent vanes defining an inlet
area of the impeller over their entire radial dimension
and being generally planar;
said third edges of adjacent vanes defining an
outlet area of the impeller; and
said outlet area being greater than said inlet area.
A molten metal pump impeller comprised of an
imperforate substantially circular base having a surface
including a hub adapted to receive a shaft, at least two
imperforate vanes connected to and extending
substantially perpendicular from said surface and
extending radially from said hub toward a peripheral
portion of said base, said vanes being spaced
circumferentially apart;
each vane defining a first edge, a second edge and a
third edge;
said first edge being disposed on said base;
said second edge defining an inlet end;
said third edge being a radially outer edge;
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said second edge of adjacent vanes defining an inlet
area of the impeller over their entire radial dimension
and being generally planar;
said third edges of adjacent vanes defining an
outlet area of the impeller; and
said outlet area being greater than said inlet area.
BRIEF DESCRIP~ION OF THE DRAWINGS
Figure 1 is a cross-sectional view of a molten
metal pump;
Figure 2 is a cross-sectional view of an
impeller attached to a drive shaft for use in a molten
metal pump;
Figure 3 is a cross-sectional view of the
impeller of Figures 1 and 2;
Figure 4 is a cross-sectional view of an
impeller having curved vanes;
Figure 5 is a cross-sectional view of impeller
designs operable in a molten metal pump; and
Figure 6 is a sketch of a relieved four vaned
impeller.
DETAILED DESCRIPTION OF THE INVENTION
While the invention will be described in
connection with a preferred embodiment, it will be~
understood that it is not intended to limit the invention
to that embodiment. On the contrary, it is intended to
cover all alternatives, modifications, and equivalents as
may be included within the spirit and scope of the
invention defined by the appended claims.
Referring now to Figures 1 and 2, a molten
metal pump according to the invention is indicated
generally by the reference numeral 20. The
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pump 20 is adapted to be immersed in molten metal contained within a vessel
5 (not shown). The vessel can be any container containing molten metal.
It is to be understood that the pump 20 can be any type of pump
suitable for pumping molten metal. Generally, however, the pump 20 will
have a base member 38 within which an impeller 40 is disposed. The
impeller of Figures 1, 2 and 3B is a cross-sectional view "X"-"X" as shown in
10 Figure 3A. The impeller 40 is supported for rotation within the base member
38 by means of an elongated, rotatable shaft 30. The upper end of the shaft
30 is connected to a motor (not shown). The motor can be of any desired
type, for example air or electric. The pump 20 is supported by means of posts
18, post sleeves 16 and a support plate 24 attached via post sockets 21.
The base member 38 includes an outlet passageway 48. A
riser may be connected to the base member 38 in fluid communication with
the passageway 48. The pump 20 is best described as a so-called circulation
pump, that is, it circulates molten metal within the vessel. As indicated
earlier, however, the pump 20 is described for illustrative purposes and it is
understood that the pump 20 can be of any type suitable for pumping the
molten metal. The base member also includes a baffle plate 50 and a shaft
mount bearing 51.
The impeller 40 is secured via cement, such as FraxsetTM,
obtainable from Metaullics Systems Division. A first bearing ring 42 of silicon
2 5 carbide or other material having bearing properties at high temperature isdisposed about the lower most end of the impeller 40. A second bearing ring
of silicon carbide or other material having bearing properties at high
temperature is disposed at the lower most end of the base member in facing
relationship to the first bearing ring 42.
As will be apparent from the foregoing description, the impeller
40 is rotatable relative to the base member 38. The bearing rings 42 and 44
will prevent friction related wear of the base member 38 and the
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impeller 40 from occurring. This base member 38 includes volute case 39
5 within which the impeller 40 is disposed.
The upper, or first end of the drive shaft 30 projects from the
first end of shaft sleeve 28 and is connected to the motor 60 via coupling
assembly 54, as shown in U.S. Patent No. 5,092,821. Preferably, the drive
shaft is of a quadralobal nature, as described in U.S. Patent No. 5,092,821.
In addition to cement attachment of the impeller to the drive
shaft 30, the impeller is secured to the drive shaft via graphite dowel pins 80.The impeller is further secured to the shaft 30 via a back-up sleeve 82 which
acts as reinforcement to the attachment joint and as a locator for the impeller.Both of these embodiments are covered in U.S. Patent No. 5,025,198. A
further bearing ring 84, comprised of silicon carbide or other thermally
resistant bearing material, encircles the upper most portion of the back-up
sleeve 82. This bearing ring 84 will be opposed by another bearing ring 86
within the base member 38. The back-up sleeve 82 is generally affixed to the
shaft 30 and prevented from upward movement via a collar ring 88A on the
shaft 30.
Referring now to Figures 3A and 3B, the impeller 40 is shown as
a four-vaned circular base impeller. Typically, the impeller consists of a
circular base 88 topped by at least two vanes 90. Vane generally means a
flat or curved object rotated about an axis that causes or redirects fluid flow.In addition as used herein, vane means an independent surface imparting
work on the molten metal. The upper portion of the impeller contains an
opening 92 for acceptance of the lower end of the shaft 30. The impeller has
a recessed based portion 96 for attachment of a silicon carbide bearing ring
42. Typically, the vanes are tapered with the thickest section beginning at the
30 center most portion of the impeller adjacent the shaft. The tapering and the
thickness of the vanes are important features with regard to wear from
inclusions and/or sediment in the molten metal and molten metal fluid volume.
Particularly, the thickness and the dimensions facilitate the durability of the
vanes under stress.
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Figure 4 demonstrates the i",pe"er of a molten metal pump
5 including curved vanes in an offset design. These alternatives may further
reduce the degradation to the impeller by particles in the molten metal.
Figure 5 demonstrates various forms of the impeller of the
molten metal pump may take to achieve the objects of the invention.
rlefer;lbly, the impeller is dynamically balanced. Figures 5A and 5B
10 demonstrate that the impeller need not specifically contain vanes. In fact, any
geometric shape (square, rectangle, triangle, star) will effectively force
directed molten metal flow. Although the efficiency may be reduced by the
limited fluid volume between the sides of the square and the circular radius
created by the spinning corners, this design would demonstrate high strength
15 and ease of manufacture. Sides as used herein means the surfaces
generally parallel to the shaft axis. Fluid volume as defined herein means the
volume of the impeller which fills with molten metal during operation,
demonstrated by the shading of Figure 5B.
Figure 5A shows that a circular base portion is only a preferred
20 embodiment. The base portion functions to direct the fluid flow into the
impeller from the top and to discharge the fluid in a direction perpendicular tothe rotating shaft. The base portion may also be the portion of the impeller
located nearest the shaft and the top of the pump, in which case the pump is
a bottom feed unit (Figure 4). Without a base plate, the pump draws molten
2 5 metal from both top and bottom. This embodiment would decrease efficiency
in exchange for ease of manufacture. A second purpose of the base plate is
to hold a bearing ring, also a preferred embodiment. Figures 5C, 5E, and 51
demonstrate an impeller without a base plate.
Figure 5D demonstrates an impeller having tapered vanes to
30 achieve a strong central portion for shaft attachment and increased fluid
volume. Figures 5A, 5F and 5G demonstrate the flexibility of this impeller
design, wherein, the impeller can contain a minimum of two vanes (5H) to a
very high number of vanes as demonstrated by Figure 5G. A low number of
vanes, as in Figure 5H, creates a very high fluid volume,
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however, there may be some loss of effficiency due to a reduced force on the
5 fluid at points distant from the two vanes.
Figure 5J demonstrates curved vanes and contouring of the
vanes to maximize strength and to reduce wear. Note, however, that
curvature of the vanes limits the pump to unidirectional use. Vanes which are
thicker in areas (vane bottoms in Figure 5J) may resist wear at those points
10 where contact from molten metal and particles therein is the most severe.
The use of thin sections again increases the fluid volume and improves
efficiency.
Figure 6 demonstrates an alternative means of increasing
pumping capacity. Relief of a portion of the vanes near the shaft/hub
15 provides increased fluid access, however, mechanical strength is somewhat
reduced.
It will be appreciated from the foregoing descriptions that the
molten metal pump according to the invention, possesses the advantages of
high effficiency and durability. Particularly, the impeller in relationship to the
2 0 described shaft and motor mechanism is effective in the transfer of molten
metal with reduced clogging and/or catastrophic failure.
Thus it is apparent that there has been provided in accordance
with the invention, a molten metal pump that fully satisfies the objects, aims,
and advantages set forth above. While the invention has been described in
25 conjunction with specific embodiments thereof, it is evident that many
alternatives, modifications, and variations will be apparent to those skilled inthe art in light of the foregoing description. Accordingly, it is intended to
embrace all such alternatives, modifications, and variations as fall within the
spirit and broad scope of the appended claims.
